Cold cathode gaseous discharge device for producing electrons in an x-ray fluorescence analysis apparatus

ABSTRACT

Examination of the composition of a preparation by means of Xray fluorescence is difficult in the case of elements of lighter weights. An improvement is achieved by causing the preparation to produce X-rays from the lighter-weight elements by the bombardment of slow electrons, produced in a gas discharge, the cold cathode and the preparation space forming an equipotential space. Gas released from the preparation then has little influence.

United Etates Patent [191 Houtman et a1.

[ Dec. 3, 1974 COLD CATHODE GASEOUS DESCHARGE DEVICE FOR PRODUClNG ELECTRONS IN AN X-RAY FLUORESCENCE ANALYSES APPARATUS [75] Inventors: Eliberthus K-lloutman; Jakob Gerard Siekman, both of Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

York, NY.

[22] Filed: Mar. 7, 1973 [21] Appl. No.: 338,869

Related US. Application Data [63] Continuation of Ser. No. 121,392, March 5, 1971.

[52] US. Cl 250/310, 250/272, 250/399 [51] Int. Cl. G011n 23/22 [58] Field of Search 250/272, 279, 306, 307,

[56] References Cited UNITED STATES PATENTS 2,924,715 2/1960 Hendee et al 250/279 3,155,827 Nixon 250/310 3,307,066 2/1967 Shapiro et 211.... 250/310 3,346,736 10/1967 Neuhaus 250/310 3,374,349 3/1968 Macres 250/310 3,435,211 3/1969 Softky 250/272 Primary ExaminerWilliam F. Lindquist Attorney, Agent, or Firm-Frank R. Trifari [5 7 ABSTRACT 8 Claims, 1 Drawing Figure Nt i PAH-INTEL mi 31m 3.852.596

' f g\\\ 10 a INVENTORS iL/QR-LQ AG ENT heated electron source and the specimen to be examined are arranged in one exhausted space in which a low gas pressure prevails.

Such a device is known from US. Pat. No. 3,435,211. The specimen is lying on the anode formed by a flat disc held by a supporting rod. The cathode is formed by a: hollow ring located substantially opposite the rear side of the anode and supported by a cylinder. Between this cylinder and the anode supporting rod there is arranged a cylindrical insulator. The X-rays produced in the specimen are projected through a thin window and a collimator onto an analyzing crystal. The discharge between the electrodes is produced by means of a direct voltage or a highfrequency alternating voltage.

This known arrangement has the disadvantage that because of the small distance between the electrode gas released by the specimen due to a high vapour pressure thereof may drastically affect the discharge and may particularly renderit unstable. i

The invention-has for its object to mitigate the disadvantages of the known arrangement.

According to the invention in a device for examining material by means of X-ray fluorescence,.in" whichthe non-heated electronsou'rce and the specimen to be examined are located in one exhausted space in which a low gas pressure prevails, the ele'ctron beam emerging from the cathode is guided through a hollow cylinder, behind which the specimen is located in an equipotential space so that the electrons travel along substantially straight paths, while the gas pressure is of the order of to 10" Torr.

Since the anode is formed by a hollow cylinder, the communication between the discharge space and the space accommodating the specimen is so large that the degree of vacuum in both spaces'is the same. On the other hand the communication has such a flow resistance that impurities originating from the specimen can penetrate only with difficulty into the discharge space between the anode and the cathode. Also higher gas expulsions from the specimen can hardly affect the discharge. According to the invention the specimen space may be traversed, if desired, by a flushing gas of the same pressure as required in the discharge space, if necessary with addition of'flushing gasthrough the discharge space. In the arrangement embodying the invention it is possible, for example, to dispose in the specimen space a sample of a steel melt shortly after solidifience to the drawing, which shows schematically a device embodying the invention.

A metal bottom 1 is secured by means of a stuffing modates the cathode 4 formed by a block of aluminum, copper or a similar metal. The cathode is surrounded for the major part by a grid 5; the distance from the cathode is 1 mm and the mesh of the grid is 2.5 mms. By means of a sealing ring 6 the cylinder 3 is secured to the cylindrical anode 7, which is directly connected with the walls defining the specimen space 8. A lid 9 With-a sealing ring 10 covers an opening in the specimen space. Two supports 11 hold the specimen 12 in a manner not shown in detail. The X-rays produced from the specimen by theelectron beam from the cathode 4 are guided through the collimator 13 to the analyzer 14.

The pressure in the vacuum space lies between 10' and 10' Torr of air or dry nitrogen. The pressure is maintained by pumping through the tube 16 and, if necessary, by allowing the gas concerned to leak in through 17 or 18.

The grid is connected via a capacitor 19 and a resistor 20 to the cathode. A direct voltage of 15 to 30 kV is applied to the terminals 21. The grid 5 takes a charge of 2 to 4,kV positive to the cathode. The discharge current is 1 to 2 mA and satisfactorily stable owing to the self-adjusting grid.

By arranging the specimen with its surfaceperpendicular to the electron beam and enlarging the distance between the anode 7 and specimen 12, ample space may be provided for accommodating a number of analyses for difierent elements in the specimen.

What'is claimed is:

1. Apparatus for causing X-rayfluorescence of the surface of a materiaLcomprising:

walls defining a first chamber, a second chamberand a straight channel connecting said chambers, said walls forming a gas tight enclosure and the walls defining said first chamber and said channel being electrically conductive; an exhaust outlet in saidfirst chamber for exhausting gas therefrom to establish and maintain a low gas pressure in'side said enclosure, said low gas pressure being within a range suitable for establishing and maintaining a cold cathode gas discharge within said enclosure; I anon-heated cathode disposed within said second chamber opposite said channel; means for electrically connecting between said nonheated cathode and said walls defining said channel a source of sufficiently high voltage to establish and maintain a cold cathod gas discharge between said non-heated cathode and said channel, thereby causing an electron stream to travel through said channel intosaid first chamber; and

means for supporting a material within said first structure being electrically connected to said nonheated cathode through a parallel combination of resisring 2 to a ceramic cylinder 3. The cylinder 3 accomtance and capacitance, said grid structure acting to stabilize the gas discharge.

6. Apparatus as defined in claim 1 wherein the residual gas remaining in said enclosure at said low gas pressure is substantially air or substantially nitrogen.

7. Apparatus as defined in claim 1 further characterized by a gas inlet in said first or second chamber for leaking gas into said first or second chamber to continuously flush from said enclosure gases released from the material supported for X-ray fluorescence.

8. Apparatus as defined in claim 7 wherein the gas leaking into said enclosure through said inlet is substantially air or substantially nitrogen.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,852,596 DATED December 3, 1974 INV ENTORG) I ELIBERTHUS HOU'Il LAN ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the title page, after section [21] insert the following:-[30] Foreign Application Priority Data March 20, 1970 Netherlands ..7003972- Signed and Scaled this Fourteenth Day of December 1 976 [SEAL] A ttest:

RUTH C. MASON Arresting Officer 

1. Apparatus for causing X-ray fluorescence of the surface of a material, comprising: walls defining a first chamber, a second chamber and a straight channel connecting said chambers, said walls forming a gas tight enclosure and the walls defining said first chamber and said channel being electrically conductive; an exhaust outlet in said first chamber for exhausting gas therefrom to establish and maintain a low gas pressure inside said enclosure, said low gas pressure being within a range suitable for establishing and maintaining a cold cathode gas discharge within said enclosure; a non-heated cathode disposed within said second chamber opposite said channel; means for electrically connecting between said non-heated cathode and said walls defining said channel a source of sufficiently high voltage to establish and maintain a cold cathod gas discharge between said non-heated cathode and said channel, thereby causing an electron stream to travel through said channel into said first chamber; and means for supporting a material within said first chamber in the path of said electron stream, the surface of a material supported thereby and exposed to said electron stream being caused to X-ray fluoresce.
 2. Apparatus as defined in claim 1 further characterized by a grid structure substantially surrounding said non-heated cathode, said grid structure having an aperture positioned directly between said cathode and channel to allow a gas discharge therethrough, said grid structure being electrically connected to said non-heated cathode through a parallel combination of resistance and capacitance, said grid structure acting to stabilize the gas discharge.
 3. Apparatus as defined in claim 1 wherein the walls of said channel are maintained at an electrical potential between 15 and 30 thousand volts more positive than said cathode.
 4. Apparatus as defined in claim 1 whereiN the walls defining said first chamber are in electrical contact with the walls defining said channel and the walls defining said second chamber at least in the vacinity of said channel are insulative.
 5. Apparatus as defined in claim 1 wherein said low gas pressure maintained within said enclosure is on the order of 10 2 or 10 1 Torr.
 6. Apparatus as defined in claim 1 wherein the residual gas remaining in said enclosure at said low gas pressure is substantially air or substantially nitrogen.
 7. Apparatus as defined in claim 1 further characterized by a gas inlet in said first or second chamber for leaking gas into said first or second chamber to continuously flush from said enclosure gases released from the material supported for X-ray fluorescence.
 8. Apparatus as defined in claim 7 wherein the gas leaking into said enclosure through said inlet is substantially air or substantially nitrogen. 